Average snub velocity loss

[Tony_the_tiger]

I've read a few different threads but I'm interested if any of y'all have calculated a mean velocity loss by barrel length. There seems to be several factors at play such as make/model of firearm, bullet weight and construction, powder load, and others.

Specifically, I've been looking at the 158 grain gold dot. Speer publishes a velocity of 1235 ft/s out of a 4" barrel. Underwood pushes the same bullet to a reported 1475 ft/s out of a 4" barrel. I'm curious as to what velocities these rounds might be expected to produce out of a 2" barrel.

Additionally, what factors other than velocity and accuracy might contribute to bullet performance? Will a bullet traveling 1200 ft/s out of a 4" barrel and a bullet traveling 1200 ft/s out of a 2" barrel perform exactly the same, all other factors being equal?

I'm not interested in a debate about recoil, I'm just curious as to your experience with velocity loss due to barrel reduction with this load and others.

Thanks!

-Triple+T

 

[rswartsell]

The rule of thumb I have heard and think makes sense is 50fps. per inch of barrel (as pertains to .38/.357) all else equal.

Hollow point "blooming" and bullet expansion are both tied directly to velocity, as well as material contacted, day of week, phase of moon, mother's last name, etc.

 

[rswartsell]

oops, forgot how you hold your jaw at detonation!

 

[Averageman]

I always figured that a snub nose velocity loss was essentially the equal of one caliber down.
I know thats not very scientific, but looking at it, it isn't a bad rule of thumb.

 

[rswartsell]

Seriously,

The 50 fps. per inch is what I have heard, and velocity will be the major factor in "bullet performance". To get beyond that the individual firearm would need to be tested and the list of "possible" factors determining specific performance gets into practical physics and could be endless. For your purposes the bullet mounted was designed under certain defined parameters such as medium you shoot into to perform well at certain velocity limitations. Considering other factors gets beyond the average laymans abilities and resources very rapidly.

 

[duns]

Take a look at this web site for hard data
http://ballisticsbytheinch.com/

 

[R.W.Dale]

Take a look at this web site for hard data
http://ballisticsbytheinch.com/

BBTI doesn't really help much with revolvers due to the discrepancy as to how a revolver barrel and their single shot barrels are measured.

A revolver barrel is from the cylinder forward.

Everything else measures to the breachface.

 

[56hawk]

Not sure where the 50 fps per inch came from, and if you notice from the above link velocity and barrel length are not linear. There is a huge difference going from a 2" to a 3" barrel, and very little difference going from a 9" to a 10". Anyway with my reloads I get 1200 fps from a 4" 686 and 925 fps from a 1 7/8" M&P 360.

 

[rswartsell]

Agreed Hawk,

The "rule of thumb" came from comparing common barrel lenghts (2-6"), common firearm properties (cylinder gap, rate of twist, ad. infinitum) and common loads in the .38/.357 category. Specific answer to the question in a nutshell just isn't possible.

 

[Tony_the_tiger]

I hope your right, rswartsell. The ballisticsbytheinch data for .357 magnum indicate an average loss of 475 ft/s from a 4" to 2" barrel. That is pretty remarkable loss... I have trouble believing that a 2" barrel reduction could account for approx. 1/3 of a rounds velocity...

 

[R.W.Dale]

I hope your right, rswartsell. The ballisticsbytheinch data for .357 magnum indicate an average loss of 475 ft/s from a 4" to 2" barrel. That is pretty remarkable loss... I have trouble believing that a 2" barrel reduction could account for approx. 1/3 of a rounds velocity...

Again note the difference in how a barrel is measured ..

BBTI's 2" barrel is literally a 357 magnum chamber + .5" of course the velocity loss is huge

A 2" snubby revolver actually has an effective barrel length closer to 4"


http://www.thehighroad.org/showthread.php?t=664754
This recent thread of mine has quite a bit of comparison data for various barrel lengths

 

[rswartsell]

whatever, the gist of my posts have been that the variables involved are too numerous to mention and that anyone's "rule of thumb" or even their tables may not have direct bearing on what you personally experience. The variables are too numerous for your questions to have a specific answer here. But hey, I'm an easy guy so I will cheerfully refund the price of entry now. That better?

BTW, speed of powder burn, gas checked bullet?, specific diameter of bore, on and on...

P.S. 475 fps per 2 inch? Really? THAT my dear friend indicates a load designed to burn A LOT of the load in the third and fourth inch. A factor that (not included in your initial ruminations) is now possible with modern powder blending techniques of multi-million dollar (or thereabouts) load development programs. And you are asking for a standard that can be applied to all loads (or at least 2 that don't necessarily have many commomn traits). And you hope I am right, well....

 

[Tony_the_tiger]

I absolutely appreciate your feedback and experience in this thread. I'm thinking I should just chrono the rounds

On the other hand I think a 158 grain gold dot .357 anywhere from 950 - 1400 ft/s performance should be largely academic...

 

[rswartsell]

especially since Gold Dots have one of the best reputations in the business for expansion, weight retention, and "petaling". The Speer GD "Short Barrel" loads are a perfect example of what is now possible with high tech powder blending and very expensive load development programs.

 

[Tony_the_tiger]

Data from the link R.W. Dale provided indicate a mean loss of 134 ft/s when shooting a 4" Gp100 followed by a 2" LCR. Thats certainly more optimistic than initial estimates...

 

[Steve C]

The aproximate 50 fps per inch is a very good estimate and has been proved true for many different loads I've ran over my chrono from both long and short barreled guns. You do find quite a bit of variation between guns of the same barrel length, some guns that shoot slow and some that shoot fast so there's no hard rule regarding how much velocity you will loose or gain.

 

[Rexster]

NYPD has had good street results with the .38 +P Speer Gold Dot Short Barrel load. The .357 version is only a bit faster, but I figure that little bit can only help me, so when I can find it, I buy it.

Whenever feasible, I carry my 3-1-16" SP101, or a larger weapon, to accompany my 24/7 "always" 2.25" SP101, because, over time, I have seen chronograph results, of various loads, showing quite a bit of velocity loss when .357 Mag is fired from barrels less than 3
inches in length. Really, though, I don't lose any sleep over this velocity loss, as shot placement is so very paramount, and the sound and fury of a .357 in a bad guy's face is certainly not going to make things easy for him. Gun writer Darryl Bolke once described the SP101 as a "hand-held flash-bang," and opined that one reason for the .357's formidable reputation for stopping power is that a bad guy really does not want that thing to be going off in his face a second time. (I have paraphrased this from memory.)

To be clear, I do use weapons other than magnum snubbies, too, and would, given the opportunity, select a different handgun than a magnum snubby for many circumstances. I would rather, for example, engage at night with a full-sized 1911 in my hands.

 

[1911Tuner]

Will a bullet traveling 1200 ft/s out of a 4" barrel and a bullet traveling 1200 ft/s out of a 2" barrel perform exactly the same, all other factors being equal?

Sure. Why wouldn't it? The bullet doesn't know what barrel length it came from.

 

[jmr40]

I have trouble believing that a 2" barrel reduction could account for approx. 1/3 of a rounds velocity...

Why not? Going from 4" down to 2" is a 50% reduction in barrel length. Going from 8" down to 6" would only be a 25% reduction in barrrel length and would result in far less velocity loss.

Bullets start out slow and their speed increases as barrel length increases. When cut extremely short they never get a chance to build up speed. You eventually reach a point where velocity gains are small enough to not worry. But that does not happen in handguns. A 357 reaches that point at around 16-18". It will still shoot faster from longer barrels, but the gains are very small beyond that.

You will see wide ranges of velocity from different guns. Often more than 100 fps from seemingly identical guns with equal barrel lengths firing ammo from the same box. This complicates making comparisons.

Some chamberings are more efficient from short barrels than others. The 357 is one that needs longer barrels. Even from 4" barrels a 357 will just barely outperforms typical 9mm from 4" barrels. Start shooting 357 from barrels shorter than 4" and a typical 9mm becomes a more powerful round. A 357 is at it's best from 6"+ barrels and when firing heavier bullets.

 

[1911Tuner]

I have trouble believing that a 2" barrel reduction could account for approx. 1/3 of a rounds velocity.

It doesn't. Depending on the powder burn rate, about 90% of the bullet's exit velocity is realized within an inch of travel in the barrel. With some really quick powders like Bullseye and HP-38, it comes before the base of the bullet has even cleared the case mouth, and with quick powders and longer barrels, it's even possible for the bullet to be moving faster as some point in the barrel than it is at the muzzle.

The loss per inch is also burn rate dependent. Slow powders lose more per inch than quicker ones, all else assumed to be equal. Even rifle powders reach peak pressure and velocity within about 3-4 inches of bullet travel.

Let's look at a simplified hypothetical gun/ammo combo.

With the typical powders used in the .45 Auto firing a 230-grain RN at standard velocities loses about 30 fps per inch of barrel. A 5-inch gun has about 4.1 inches of rifled barrel. Let's call it 4 inches to keep it simple. In this gun, 120 fps is realized in the barrel. If we start with 830 fps...that leaves 710 fps unaccounted for.

 

[KeithL]

The bottom of each of those calibers is a chart of real world firearms. In some cases the snub did better by than the test barrel, but not by much. The difference is definitely greater than 50 fps/inch in the short barrels (in the longer barrels it seems to be pretty close). The difference is significantly more as the barrel length decreases.

 

[PabloJ]

Not sure where the 50 fps per inch came from, and if you notice from the above link velocity and barrel length are not linear. There is a huge difference going from a 2" to a 3" barrel, and very little difference going from a 9" to a 10". Anyway with my reloads I get 1200 fps from a 4" 686 and 925 fps from a 1 7/8" M&P 360.

Barrel length vs. Velocity by Bob Milek in Outdoor life 'Guns & Shooting Yearbook' 1990. Several good article in there well worth tracking down.

 

[Hondo 60]

I have 2 - 357 Magnums & 3 - 38 Specials, a 4" & a 2" of each.
I consistently get ~100fps less with the 2 inchers vs the 4 inchers.

With one of my wimpier 357 loads I get about 1000fps from my 4" S&W 65-2.
With the same load I get about 900 fps with my Ruger Sp101 (2.25" barrel)

Likewise my standard 38 Special load produces about 850 fps outta a S&W 10-5 (4")
versus 700-750 fps from a S&W M38 & a Charter Arms Undercover (both are snubbies)

 

[56hawk]

Barrel length vs. Velocity by Bob Milek in Outdoor life 'Guns & Shooting Yearbook' 1990. Several good article in there well worth tracking down.

Tried to find it online, but only found parts of the article. Would be interested to find out what 357 he cut down and what lengths were tested. I looked at the ballistics by the inch data and it's not even close to 50 fps per inch for short barrels. Closer to 100-200 fps per inch. It did average out to 58 fps per inch when looking from 18" down to 2" though.

 

[Tony_the_tiger]

Its very interesting to note the different velocities posted by forum members with chronographs, those posted by writers, and those published by manufacturers. As rswartsell noted the list of confounding factors is potent and I do not see a valid statistical method to predict velocity loss based solely on barrel length, bullet weight, and caliber.

That said, I spoke to the owner of Underwood today. They push the 158 grain gold dot that speer loads at 1235 ft/s out of a 4" barrel up to 1475 ft/s out of a 4" barrel.

I had five questions:

a)is the load within pressure specs for the cartridge? His reply was yes, it is within SAAMI spec.

b) what is the expected velocity loss from 4" to 2"? He said that out of a 4" they got 1475 ft/s. Out of a 3" they got 1395 ft/s. They had no data on 2".

c) Do you use particularly slow burning powders? His reply was no, they have pretty fast burning powders in that round. He went on to note that he expects the velocity gains achieved in comparison to the speer loading out of a 4" tube to hold true in smaller barrels.

d) Do you have any history of issues with the ammo or double charges? He replied "honestly, I can say that we have never blown up a gun... (yet) <--- parenthesis added by original poster and not directly quoted.

FYI, and as noted by other posters, the "Barrel by the inch" data seems to have internal validity but I wonder if it is relevant to this topic especially given the points R.W. Dale noted.

In the meantime, I'll give the underwood round a try. I already use short barrel gold dots and .38 rounds in a 442 and am looking for something a bit stouter in a steel J frame .357.